1. Field of the Invention
The present invention relates to an apparatus for loading and unloading a magnetic head assembly on a magnetic recording surface and, more particularly, to a loading and retraction apparatus which permits separation of function between load retract and flying and which produces a predictable pitch to the magnetic head assembly in the static condition and no pitch bias in the dynamic flying condition.
2. Description of the Prior Art
Magnetic disc storage systems are widely used to provide large volumes of relatively low cost computer-accessible memory or storage. A typical disc storage device has a number or storage. A typical disc storage device has a number of discs coated with a suitable magnetic material mounted for rotation on a common spindle and a set of transducer heads carried in pairs on elongated supports for insertion between adjacent discs, the heads of each pair facing in opposite directions to engage opposite faces of adjacent discs. The support structure is coupled to a positioner motor, the positioner motor typically including a coil mounted within a magnetic field for linear movement and oriented relative to the discs to move the heads radially over the disc surfaces to thereby enable the heads to be positioned over any annular track on the surfaces. In normal operation, the positioner motor, in response to control signals from the computer, positions the transducer heads radially for recording data signals on or retrieving data signals from a preselected one of a set of concentric recording tracks on the discs.
As the density at which digital information is recorded on a magnetic recording surface is increased, the gap between the recording head and the magnetic recording surface must be decreased. The smaller the gap and the closer the magnetic head is positioned with respect to the recording surface, the more difficult it becomes to control the mechanical tolerances of the structure mounting the recording head. To overcome these mechanical difficulties, magnetic recording heads are placed in head assemblies adapted for floating on a thin film of air created by the laminar air flow due to the rotation of the recording surface. Modern magnetic disc drives incorporate rigid substrate discs, the surfaces of which are polished to a high finish so that the head can reliably fly on the air bearing. Systems are presently being designed wherein the heads fly above the disc recording surfaces at heights of less than 20 microinches.
In such systems, when the recording medium rotates, the laminar air flow causes the head assembly to be forced away from the medium. Therefore, some urging means, such as a spring, must be provided to overcome this air flow and counterbalance the head assembly, keeping it as close to the recording medium as possible. Furthermore, floating magnetic recording head assemblies are often mounted in gimbal mounting devices in order to allow the angle and position of the magnetic recording head assembly to conform to the air bearing. The above is well known to those skilled in the art.
One known and popular magnetic head/arm assembly is the IBM type 3370 which is disclosed and claimed in U.S. Pat. No. 4,167,765 to Robert B. Watross. According to the IBM design, a magnetic head/arm assembly has a suspension for an air bearing head slider that includes a single piece, substantially rectangular flexure with two parallel, flexible, narrow fingers, a relatively stiff cross leg, and a central finger to which the slider is attached. A combined load beam/spring element is formed from a single piece and is fastened to the flexure so as to engage a load protuberance formed with the central finger. The substantially triangular load beam/spring element has flanges formed along a portion of its length to concentrate the resilient spring action at the opposite end of the element while providing a stiffening action along the remaining portion of its length. The opposite end is connected to a rigid arm section.
The IBM design, as shown in the Watross patent, is not loadable, i.e. it includes no means for removing the head slider from the disc. Since this is often undesirable, the IBM design has been modified by adding a central protrusion which extends downwardly from the bottom thereof and which is activated by a fixed cam which spans the whole structure. This permits the magnetic head assembly to be lifted off of the recording surface upon retraction of the arm assembly.
While the IBM type 3370 head assembly is quite popular, several problems are associated with the loadable version thereof. The first is that retraction of the slider is limited in its motion. That is, the fixed cam extends below the load beam, in position to be contacted by the central protrusion which extends downwardly from the bottom thereof. As the load beam is retracted, the central protrusion passes the cam and if the load beam were continued to be retracted, the head slider would contact the fixed cam. Even by placing the central protrusion and the fixed cam as close to the rear of the load beam as possible, retraction of the slider is still significantly limited. As a result, it often occurs that discs strike the head slider upon being inserted into a system, causing damage to the slider. This problem results from an inability to fully retract the head slider.
A second problem is a poor ratio of lift point to load beam bending point, resulting in poor load zone tolerances on the disc. That is, becuase of the necessity of putting the central protrusion quite close to the rear end of the load beam, slight misalignments of the load beam bending point and the fixed cam result in significant movements of the head slider. The result is that a large load zone area on the disc is required and this is undesirable since data is typically not recorded in the loading zone.
A still further problem results from the inability to acceptably control the pitch of the head assembly and to separate the functions during dynamic and static conditions. That is, the loadable version of the IBM design strictly provides for loading and unloading so that the pitch of the head assembly must be controlled separately.
One technique for controlling the pitch of a head assembly and separating the functions during dynamic and static conditions is disclosed in U.S. Pat. No. 4,376,294, entitled Head Loading and Retraction Apparatus for Magnetic Disc Storage Systems, and assigned to DMA Systems Corporation, the assignee of the present invention. However, the head loading and retraction apparatus disclosed in such patent is not feasible for use with the IBM type 3370 magnetic head/arm assembly.